I came across this design from Alexander Seewald a while back for a “bluetooth-enabled remote control car” that could be controlled with a Nokia series 60 bluetooth cellphone. I thought this was pretty cool, but then I thought, why not take it to the logical next step: why not have the phone be part of the car instead of just controlling the car. I’ve been working on a design for this, I’m going to be updating this with a lot more information and source code as time goes on. For now I’m going to start by going over the different components of the design.
Here’s what you need:

A Symbian OS Series 60 phone — these are primarily Nokia phones, you can get a used lower-end one on Ebay. These are all GSM phones, so you can use them with any GSM-based cell carrier; just pop in your SIM card.

The N95, despite it’s $550 price tag, is quite attractive for mobile robotics platforms because of features like:

Other much cheaper Series 60 phones can also be used for robotics — for instance the Nokia 6620 goes for about $120, it still has bluetooth, a camera, and internet support.

A cellular plan (I am currently using AT&T Wireless) with unlimited internet access is probably a good idea, although with some of these phones you can also use free wifi.

Pys60 installed on the phone- this is the Python programming language for Series 60 phones. I used this instead of C++ because the development cycle is much faster/easier. This is open source software, provided free of charge.

Movino, which is a totally awesome free software cellphone-to-internet client/server video streaming system. Movino has a part that runs on the phone which captures video and audio from the phone’s camera and mic and sends it to the server, which can then stream it to viewers live.

A Mini SSC II Serial Servo Controller from Scott Edwards Electronics Inc. He sells this for $44 — I recommend also getting the pack of “connectamundos”, wire segments with nice connectors pre-crimped onto the ends, for another $6. This comes with a snap for a 9V battery to power it, but the 9v will not power the servos — two additional leads are provided to connect to a power supply for the servos in the 4.5V – 6V range.

An eb501-SER bluetooth serial port from A7 Engineering, for $49. This is nice because it can run off a very wide range of power supplies (5.5V – 14V; you could run it off the same battery as the Mini SSC II.) and it is also very small.

Any robotics platform that utilizes standard 3-pin (PWM) hobby servos and electronic speed controllers. I found a 4wd RC car at Micro Center for $49.99 that uses an ESC to control the motor and a single servo for steering; the only problem with this platform is that it is too fast and needs to be geared down a little bit.